Heavy Quark HERA II

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1 Brian Foster Oxford University Heavy Quark HERA II DESY What s new for HERA II and what does it mean for HQ physics a reminder.. HQs in DIS, diffraction, photoproduction Spectroscopy is there a role for HERA II? Production mechanisms Single t production? Summary 1

2 HERA II Physics Both ZEUS & H1 have made major upgrades in order to utilise the increase in HERA luminosity to the full. 2

3 Vertex Region The ZEUS MVD mostly 3 layers in barrel and 4 forward wheels; > 200K readout channels. 3

4 Vertex Region H1 Si 2 very thin CST layers; 5 disks covering 8 < θ < 17 o 4

5 Forward Physics ZEUS major upgrade in forward direction replacement of TRD s with two stations of straw-tube chambers, each with 3 stereo layers. H1 have made improvements to various parts of their tracking systems. FTD1 FTD2 FTD1 CTD 5

6 Forward Physics H1 forward disks Extends charm coverage to higher x similar improvement for ZEUS Si disks and STT. 6

7 Vertex Physics H1 fast track trigger now installed and being commissioned can produce mass peaks within 100 µs. 7

8 HERA II prospects So optimistically HERA II promises factor 5 increase in luminosity, with lepton polarisation, greatly improved tracking, DAQ and triggering. This implies generally order of magnitude improvement in statistics and increased kinematic range and coverage. What does this mean for the physics reach of HERA II? 8

9 HQ in DIS HERA I has already told us a lot about the charm quark density inside the proton. 9

10 HQ in DIS Some of the open questions are obvious. 10

11 HQ in DIS Some are (much) more obscure. 11

12 HQ in DIS The promise of HERA II is great, since charm production in DIS is sensitive probe to all sorts of dynamical models. Saturation model of Kowalski & Teaney. 12

13 HQ in DIS The D* tagging method in D*? Kππ s will not be as effective (@ ZEUS) because of increased multiple scattering from the MVD. However this will be more than offset by ability to use separated vertex or large impact parameter tag, as already demonstrated at HERA I by H1. 13

14 HQ in DIS We will need substantial part of the HERA II statistics to resolve many of the interesting issues in charm in DIS, even with substantial improvement in tagging efficiency. Thorne, Roberts 1998 The mechanism to take charm mass into account can give substantial mods. to theoretical expectation as function of Q 2 at higher x. Intrinsic charm can also modify these predictions but unlikely we can get useful info. on this at HERA II. 14

15 HQ in DIS Very precise measurements of F 2 c will be possible for HERA II; also gives accurate gluon determination and cross-check with the more global QCD fits pb pb -1-1 Accurate b contribution to F 2 will become possible cross-check of VFNS and clean test of photon-gluon fusion process. 15

16 HQ in DIS HERA II should allow both collaborations to make a full flavour decomposition of the inclusive F 2 structure function. For example, charm signal in e n charged currents (expect ~ 50K events) in principle measures the s-quark density (+ leading W particles in NC etc.; but also competing non-s diagrams from c s gluon splitting in CC). p Constrain fit with s from leading φ? At HERA II, both singlet & non-singlet pdfs - u,d,s (CC DIS) & c,b,g (NC DIS) - can be determined with good accuracy. 16

17 HQ & Polarisation Polarisation in DIS will be a unique HERA II for exploring EW couplings. In principle the spin orientation of the struck quark can carry through a memory into the final-state hadron. In c and b production, one can be sure that the struck quark is in one of the c or b hadrons and there is a correlation between the detected heavy-quark hadron and the struck quark. Using weak decay of Λ c, can analyse for spin orientation of struck quark and hence disentangle spin-dependent σs. 17

18 HQ & Polarisation But first signal reported for inclusive Λ c production reported at this year s conferences, so difficult to believe that statistically significant results can be obtained via this technique. 18

19 HQ in Diffraction The structure of diffraction and its mechanism and explanation in the framework of pqcd is one of the most fruitful areas of HERA I physics. In the charm sector, very strongly limited by statistics. However, also very good discrimination amongst models one of the areas where we will most benefit from the statistics of HERA II. 19

20 HQ in Diffraction Charm production cf inclusive F 2 will also be additional constraint on gluon pdf of diffractive exchange. In exclusive processes, the heavy c quark gives clearly different behaviour to light quarks opening the relationship of QCD models of diffraction. One of the areas where one clearly sees the effect of m c as a hard scale. Again, in all of these studies, the statistics of HERA II will be decisive. 20

21 HQ in Diffraction Diffractive VM production in photoproduction now in much better agreement between H1 and ZEUS. Some statistics gain still to be expected at the highest W, and some extra kinematic reach from the extended tracking in the detectors, but generally HERA II data will not add so much to the current picture. 21

22 HQ in Diffraction Diffractive J/ψ production in photoproduction at high t sensitive tool to QCD evolution in diffraction. Again, obviously statistics limited and these type of studies will greatly benefit from HERA II data; the very distinctive final state and kinematic regime should allow efficient triggers at HERA II. Saturation models can also describe many features of J/ψ data. 22

23 HQ in Photoproduction In general statistics not a problem with photoproduction results, except where extra requirements on tagging e.g. double jet tags. However, we still have considerable work to do to understand the details even of relatively simple quantities such as inclusive differential cross sections. 23

24 HQ in Photoproduction Study of angular distributions in dijet events where one of the jets contains a D* can disentangle the dynamics of the c-production process. In principle, this method, with greatly increased statistics at HERA II, can lead to determination of c (and g) density in γ. 24

25 HQ in Photoproduction Since charm tagging works over a wide range of momenta, has rather high efficiency and high purity, charm is a useful method to look at fragmentation. The study of all these charm particles has allowed the determination of fragmentation probs. to u,d, ratios of P/V, strangeness suppression etc. to ~5 10%. This can certainly be improved at HERA II. D 0 D s D ± 25

26 HQ in Photoproduction By looking at events containing leading neutrons and a charm tag, we can get a handle on the c (& g) density in the π. This is a classic double-tag experiment which needs the increased statistics of HERA II (and more!). 26

27 B production B production both in photoproduction and DIS is really in its infancy at HERA I and will be a major study at HERA II. The most recent results from H1 & ZEUS for photoproduction imply a much smaller discrepancy between data and NLO QCD Related to differences in extrapolation from meas. σ for fully inclusive and dijet final states. 27

28 B production Good agreement between H1 & ZEUS, and with NLO QCD. However 28

29 B production Jetweb allows comparison between different experiments with implementation of experimental cuts. Comparison with PYTHIA LO +PS scaled to HERA jet σ predicts HERA & Tevatron etc. σ(b). There may still be a problem with the QCD prediction of σ(b) being too low but it is surely less than we thought and this will have to wait for HERA II. ZEUS dijet + µ 29

30 B production However, at least in DIS, we seem to have a reasonable understanding of the differential cross sections also. But we need many more than 3 bins! => HERA II. 30

31 B production One of the things we have seen start at HERA I has been the use of the vertex detectors to do vertex tagging. This will be the name of the game at HERA II. 31

32 Charm spectroscopy in γp The large HERA I data sample gave the opportunity to make useful contributions to charm spectroscopy. Rich spectrum - D 1,D 2 * established; D* seen by DELPHI, not OPAL/CLEO 32

33 Charm spectroscopy in γp However, the B and c/τ factories are now going full steam ahead and will make even the HERA II data samples insignificant e.g. in 2004, CLEO-c plans 6M tagged D decays. D 0 K 0 ηπ 0 D + Κ + Κ 0 D + π + π 0 33

34 Charm spectroscopy in CDF And that is even before thinking about CDF. For standard spectroscopy, HERA II not competitive. 34

35 Charm spectroscopy However HERA II can reach states that other machines cannot reach e.g. states coupling strongly to gluons can be copiously produced at HERA. Not obvious why such states should want to decay to charm; but then we didn t expect to see them in light-quark decays either. Pentaheavyquarks? HERA II can do charm spectroscopy we should look in those places where we are competitive. 35

36 Production mechanisms As an electron-proton collider, HERA II has access to unique production mechanisms that can provide strong tests of QCD. 36

37 Production mechanisms Rather good general agreement between Lipatov-Zotov and the data. 37

38 Production mechanisms Interplay with Tevatron can give extra constraints on relative importance of CO & CS; large uncertainties in MEs mean not so obvious that HERA II statistics very helpful without significantly more theoretical work. Inelastic J/ψ photoproduction 38

39 Production mechanisms Study of the J/ψ polarisation gives normalisationindependent information to discriminate between models. Clearly much more accurate data at HERA II required and preferably less uncertainty in theory. 39

40 Production mechanisms One process at least where we know HERA II will be vital, and which may well be a help in unraveling the J/ψ problems, is " production at HERA I we barely (?) saw elastic production, let alone inelastic. However, we probably can expect only < 100 events even at HERA II - probably not enough. 40

41 Single top production HERA cannot produce tt pairs and single production is highly suppressed in the SM FCNC process. Observation of events with high p t lepton, jet and high missing p t sensitive to this process and lots of other things. 41

42 Single top production As is well known, there is an excess of such events in H1, although not in ZEUS and not in either experiment in the hadron channel. 42

43 Single top production 43

44 Single top production Finally ZEUS sees an anomaly wrt Standard Model (?) See 2 events with p T X > 25 GeV 2 c.f. 0.12±0.02 from S.M. 44

45 Single top production This is perhaps the clearest and most important area where just the statistics gain (and the better b tagging) at HERA II will really pay dividends. 45

46 Summary Heavy quark physics at HERA I has been exceptionally rich. Not only have we measured production cross sections over wide range of Q 2, we have made contributions to QCD understanding of heavy quarks, to spectroscopy and to diffraction. HERA II promises much. There will be factors of ~5 in integrated luminosity; the tagging efficiency and kinematic reach for heavy quark measurements will increase because of the improvements to the detectors in general and the vertex detectors in particular. Many areas will benefit particularly DIS and heavy quark structure functions, and everything to do with B production. This is a very exciting prospect indeed. 46

47 Summary HERA II is starting up in earnest first data are starting to come through. The Si detectors, although being baked nicely, are not yet cooked and still there and working 47

48 Summary Background conditions under study. ZEUS - reflected synchrotron rad. greatly reduced. Particle backgrounds also look good if machine carefully tuned. Proton-related backgrounds still under study but promising. H1 vacuum conditioning worked. Need factor 3 better vacuum to run with HERA II design currents. 48

49 Summary First HQ signals starting to emerge from HERA II data. These signals from H1 the opening of the HERA II floodgates? 49

50 The WeizmannWorkshop 50

51 Summary Fingers crossed, touch wood, etc. etc. The next five or so years promise to be some of the most exciting at HERA yet. 51